Beam plasma source

ABSTRACT

A plasma source which includes a discharge cavity having a first width, where that discharge cavity includes a top portion, a wall portion, and a nozzle disposed on the top portion and extending outwardly therefrom, where the nozzle is formed to include an aperture extending through the top portion and into the discharge cavity, wherein the aperture has a second width, where the second width is less than the first width. The plasma source further includes a power supply, a conduit disposed in the discharge cavity for introducing an ionizable gas therein, and at least one cathode electrode connected to the power supply, where that cathode electrode is capable of supporting at least one magnetron discharge region within the discharge cavity. The plasma source further includes a plurality of magnets disposed adjacent the wall portion, where that plurality of magnets create a null magnetic field point within the discharge cavity.

FIELD OF THE INVENTION

The present invention relates to plasma and ion sources used forindustrial processes such as plasma treatment, plasma enhanced chemicalvapor deposition (PECVD) and plasma etching and to electric propulsiondevices for space applications.

BACKGROUND OF THE INVENTION

Plasma and ion sources are usefully applied in a number of processesincluding: Plasma enhanced chemical vapor deposition (PECVD), reactiveion etching, plasma surface modification and cleaning, increasing thedensity of evaporated or sputtered films and assisting a reactiveevaporation or sputtering process. Of growing interest is theapplication of these processes to larger substrates such as flexiblewebs, plasma televisions and architectural glass.

Several plasma and ion sources are commercially available and many morehave been disclosed. Commercially available plasma and ion sourcesinclude: Hollow cathode plasma sources, gridded ion sources, end hallion sources, closed drift type ion sources including extendedacceleration channel and anode layer types, and impeded anode types likethe Leybold Optics' Advanced Plasma Source. While successfully appliedto small substrate applications like semiconductors or optical filters,they are less effective in processing wide substrate applications. Thisis primarily due to the use of point electron sources for beam creationand neutralization rather than uniform, linear electron sources.

Point electron source technologies such as filaments, heated low workfunction materials and hollow cathodes are difficult to extend linearly.Consequently, the ion and plasma sources that rely on these pointelectron sources have difficulty producing the uniform linear beams whenutilizing large area substrates.

Therefore, there is a need for a uniform, linear plasma or ion sourcethat can be readily extended to wide substrates. This ideal linearsource should not require a delicate or expensive electron source, suchas filaments or LaB6, and should be capable of operating over a wideprocess pressure range. This source should also be physically compact,economical, and should produce a dense, efficient plasma beam.

Prior art sources generally utilize one of two technology categories.One such category comprises magnetron sputtering sources, and morespecifically unbalanced magnetrons and hollow cathode sputteringsources. The second such category comprises plasma and ion sources.

Unbalanced Magnetron Sources

Window and Savvides presented the concept of unbalanced magnetron(“UBM”) sputter cathodes in several published articles. In thesearticles, the Type II unbalanced magnetron is disclosed with its abilityto ionized the sputtered flux from the cathode. The fundamentaloperating principles of the null magnetic field region and mirrormagnetic confinement electron trapping are taught.

FIG. 12 shows a planar target type II UBM as presented by Window andSavvides. Window and Harding later disclosed a type II UBM without acentral magnetic material or high permeability pole. In FIG. 12, magnets200 are configured around the periphery of a rectangular or round shuntplate 201. Central soft iron pole 207 is located in the center of theshunt plate Because of the ‘unbalanced’ nature of the magneticarrangement, a null field point 203 is created above magnetron trap 205and strengthening field lines above the null point produce a mirrorconfinement region 208. In operation, magnetron plasma 204 sputters thetarget 206. Electrons leaving the magnetron plasma are trapped in themirror containment region 208 creating a second visible plasma region.

As presented in the literature, the mirror plasma region ionizes asignificant portion of the sputter flux from the target. The plasma 208generated in the mirror region also projects out to the substrate 209and usefully bombards the growing sputtered film. Plasma 208 can be usedfor plasma processes such as PECVD, plasma treatment etc. While findinguse in these plasma processes, the sputtered flux from the target 206 isnot always welcome, the UBM must operate in the mTorr range typical formagnetron sputtering and, for PECVD applications, the exposed target 206is quickly contaminated by condensing PECVD constituents.

Hollow Cathode Sputter Sources

The term Hollow Cathode has been used to describe a variety of sputtersources in the prior art. U.S. Pat. No. 4,915,805 discloses a hollowcathode confined magnetron with the substrate passing through the centerof the cavity. U.S. Pat. No. 4,933,057 discloses a hollow cathodeconfigured magnetron with an anode positioned opposite from the openinginto the process chamber. The anode in this position will allowelectrons to reach the anode without having to pass out of the dischargecavity first. No gas is introduced into the discharge cavity separatefrom the opening to the process chamber.

U.S. Pat. No. 5,073,245 teaches a sputter source in a cavity separatefrom the process chamber. The magnetic field is along the axis of thecavity cylinder and a magnetron type containment region is reported tobe created around the inside of the cavity cylinder walls. The openingto the process chamber creates a discontinuity in the magnetronracetrack. Anodes are located inside the cavity, at each end. U.S. Pat.No. 5,334,302 discloses a sputtering apparatus comprising multiplemagnetron cathode cavities. Process gas is introduced into the base ofeach cavity. The cavities are open to the process chamber.

U.S. Pat. No. 5,482,611 discloses an unbalanced magnetron sputtercathode with a cup-shaped or annular cathode. A null magnetic fieldpoint is produced adjacent to the cathode opening. The discharge cavityis open to the process chamber. In FIG. 6 of the '611 patent a separatemicrowave applicator is fitted over the cathode opening. Though separatefrom the cathode, the applicator opening dimensions are equal to orlarger than the cathode cavity. In one embodiment process gas isintroduced into the cavity at the base of the cavity opposite theprocess chamber opening.

U.S. Pat. No. 5,908,602 teaches a linear arc discharge source. Thedischarge cavity does not include a magnetron confined plasma region andthe discharge cavity opening is exposed to the process chamber.

U.S. Pat. No. 6,444,100 discloses a box shaped hollow cathode sputtersource. The bottom of said box is either electrically floating orconnected to the cathode. The box is open to the process chamber andprocess gas is not introduced into the box other than via the processchamber opening.

Other Plasma Sources

U.S. Pat. No. 6,444,945 teaches a bipolar plasma source, plasma sheetsource, and effusion cell utilizing a bipolar plasma source. In thepreferred embodiments a magnetron cathode plasma is not created and thehollow cathode cavity opening is exposed to the process chamber. U.S.Pat. No. 4,871,918 discloses a hollow-anode ion-electron sourcecomprising a discharge cavity with a reduced dimension opening conduitto the process chamber. There is no magnetron confined region or nullmagnetic field point within the discharge cavity.

U.S. Pat. No. 6,103,074 teaches a cathode arc vapor deposition methodand apparatus that implements a cusp magnet field. There is no magnetronconfined region inside the discharge cavity and the cavity is open tothe process chamber.

SUMMARY OF THE INVENTION

Applicant's invention includes a plasma source. Applicant's plasmasource includes a discharge cavity having a first width, where thatdischarge cavity includes a top portion, a wall portion, and a nozzledisposed on the top portion and extending outwardly therefrom, where thenozzle is formed to include an aperture extending through the topportion and into the discharge cavity, wherein the aperture has a secondwidth, where the second width is less than said the width.

Applicant's plasma source further includes a power supply, a conduitdisposed in said discharge cavity for introducing an ionizable gas intothe discharge cavity, and at least one cathode electrode connected tothe power supply, where that cathode electrode is capable of supportingat least one magnetron discharge region within the discharge cavity.Applicant's plasma source further includes a plurality of magnetsdisposed adjacent the wall portion, where that plurality of magnetscreate a null magnetic field point within the discharge cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section view of Applicant's beam source;

FIG. 2 shows a top section view of the apparatus of FIG. 1;

FIG. 3 shows an isometric view of the apparatus of FIG. 1

FIG. 4 shows a view of Applicant's beam source comprising separate gasinlets, with the beam directed toward a substrate and;

FIG. 5 shows a view of Applicant's beam source used to assist reactivedeposition in an electron beam evaporation application;

FIG. 6 shows a side view of Applicant's beam source applied to aplanetary/box coating application;

FIG; 7 shows Applicant's beam source with the plasma directed onto atranslating, biased substrate;

FIG. 8 shows two beam sources facing each other with opposite polemagnets;

FIG. 9 shows a section view of an electromagnet version of Applicant'sinvention for a space thruster application;

FIG. 10 shows an embodiment comprising an electrical power arrangementenhancing the ion source aspects of the present invention;

FIG. 11 shows a section view of Applicant's beam source implementingvertically oriented magnets and a planar cathode;

FIG. 12 shows a section view of a prior art unbalanced magnetron sputtersource.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED

FIG. 1 shows a section view of beam source 24 producing a beam of denseplasma 9 projecting outwardly from nozzle 6. Aperture 101 extendsthrough nozzle 6, into discharge cavity 26. Discharge cavity 26 has afirst width 110. Aperture 101 has a second width 115, where the secondwidth 115 is less than the first width 110. Center-line 120 comprisesthe middle of first width 110.

In certain embodiments, discharge cavity 26 comprises a parallelepipedhaving a rectangular cross section. In these embodiments, the firstwidth 110 comprises the length of the longer side of that rectangularcross section. In certain embodiments, discharge cavity 26 aparallelepiped having a square cross section. In these embodiments, thefirst width 110 comprises the length of one side of that square crosssection. In certain embodiments, discharge cavity 26 comprises acylinder having a circular cross section. In these embodiments, thefirst width 110 comprises the diameter of that circular cross section.

In certain embodiments, aperture 101 has a rectangular cross section. Inthese embodiments, second width 115 comprises the length of the longerside of that rectangular cross section. In certain embodiments, aperture101 has a square cross section. In these embodiments, second width 115comprises the length of one side of that square cross section. Incertain embodiments, aperture 101 has a circular cross section. In theseembodiments, second width 115 comprises the diameter of that circularcross section.

Source 24 is disposed within a process chamber, not shown, where thatprocess chamber is maintained at a reduced pressure. Magnets 1 and 2 aredisposed facing each other with the south poles supported by mild steelshunt 3. By “facing each other,” Applicant means that the pole of magnet1 having a first magnetic polarity has a facing relationship with thepole of magnet 2 having that same magnetic polarity. The magnets 1 and 2produce a cusp magnetic field composed of outwardly directed field lines18 and inwardly directed lines 19. The inward lines 19 pass throughinsulator 15 and liner 16 to center shunt 10. The cusp magnetic fieldcreates a null magnetic field point 25 inside discharge cavity 26. Incertain embodiments, null magnetic field point 25 is located alongcenter-line 120. Along with end magnets not shown and magnets 1 and 2,the cusp fields 18 and 19 create endless electron traps in regions 9 and8. Shunt 10 is connected to shunt 11, and both are made of mild steel.Liner 16 is brazed to block 12 to improve heat transfer.

Block 12 is water cooled via holes 13 in combination with associatedpiping not shown. Shunt 11 is fastened to block 12. The assembly of theliner 16, block 12 and shunts 10 and 11 form one electrode of thesource. The second electrode is formed by shunt box 3 and cover 5. Themagnets are ceramic type isolated from liner 16 and block 12 byinsulators 14 and 15. In certain embodiments, insulators 14 and 15 areformed from one or more fluoropolymers. In other embodiments, insulators14 and 15 are formed from an electrically insulating ceramic material.

Gap 100 separates separate box 3 from block 12 and shunt 11 to eliminateplasma in the gap. In certain embodiments, gap 100 is about 3 mm. Gas 27is introduced into the source through port 4 in box 3. The gas 27travels around block 12 via gap 100 between box and block 12; Gas 27then flows through a plurality of grooves 22 disposed in box 3 and cover5. Gas 27 is introduced into discharge cavity 26 between cover 5 andliner 16. Cover 5 includes a nozzle 6 though which the gas 27 flows intothe process chamber. The cover 5 and nozzle 6 are water cooled withbrazed-on tubing 7. One side of power supply 17 is connected to cover 5,box 3, and to chamber ground.

The other pole of power supply 17 is connected to internal blockassembly 12, and thereby liner 16 and shunts 10 and 11. The electricalconnection to block 12 is made to the water cooling tubing exiting box 3(tubing not shown). In certain embodiments, liner 16 comprises a cathodeelectrode. In certain embodiments, liner 16 is formed from materialshaving a secondary electron emission coefficient δ of about 1 or more.

In certain embodiments, power supply 17 comprises a standard sputtermagnetron type. In certain embodiments, power supply 17 comprises apulsed DC supply. In certain embodiments, power supply 17 comprises amid-frequency AC supply. In certain embodiments, power supply 17comprises an RF supply.

In the illustrated embodiment of FIG. 1, a DC supply 17 is used with thenegative electrode connected to block 12. When gas 27 is introduced intodischarge cavity 26 and power supply 17 is turned on, a plasma isignited in regions 8 and 9 of the source. Region 8 is an endless Hallcurrent contained plasma extending the length of the source. The twolobes of region 8, as seen in section view FIG. 1, appear as an extendeddonut of plasma when the inside of the operating source is viewed. Thisregion 8 is created when the electric field from cover 5 penetrates downpast magnetic field lines 19 inside the source. As electrons attempt tofollow these electric field lines they are restricted by magnetic fieldlines 19.

Electrons cannot escape from the electrostatically and magneticallyconfined region made by electron containing liner 16 and shunt 10surfaces and field lines 19. The result is a confined plasma region 8inside discharge cavity 26. Region 9 is created and sustained as aresult of plasma 8. By the arrangement of magnetic field lines 18, cover5 and nozzle 6, electrons created by plasma 8 are prevented fromreaching the cover 5 and nozzle 6 anode electrode. Field lines 18 passoutwardly from liner 16, converge, and pass outwardly through nozzle 6.

Because electrons cannot cross magnetic field lines, the electriccircuit between cover 5, nozzle 6 and plasma 8 can only be completed bythe electrons exiting through nozzle 6 and passing out of the magneticfield 18 containment region. Plasma 9 is created because, when electronsattempt to escape along magnetic field lines 18 through the nozzle 6,they are confronted with a magnetic mirror as field lines 18 converge innozzle 6. This mirror region reflects a portion of the electrons andcreates a second containment region 39 within plasma 9.

Region 39 is again a closed drift magnetic bottle as electrons move in acyclodial motion down to one end of the source and back to the other. Inaddition to the electron escape path, nozzle 6 also forms the onlyescape path for gas 27 flowing from discharge cavity 26 into the processchamber. The process gas 27 is forced through plasma region 39 where ahigh percentage of gas 27 is ionized prior to exiting nozzle 6. Theconfluence of gas 27 and electrons in region 39 creates a dense plasma 9that extends outwardly from nozzle 6 into the process chamber. When thesource 24 is viewed in operation, it appears that plasma 39 and plasma 9comprise a single plasma. The internal diameter of nozzle 6 is smallerthan the internal diameter of discharge cavity 26. By making nozzle 6narrower, not only is less sputtered material from liner 16 able toreach the process chamber, but the process gas 27 must pass throughplasma region 39 to exit discharge cavity 26.

FIG. 2 shows a top view beam source 24 with cover 5 removed. End magnets20 and 21, in combination with side magnets 1 and 2, create the closeddrift magnetic fields 18 and 19, with only magnetic field 18 shown inFIG. 2. FIG. 2 also includes box 3, liner 16, insulator 15 and, belowmagnets 1, 2, 20 and 21, water cooled block 12. Plurality of grooves 22in box 3 for gas 27 are also illustrated. Plasma 9 is shown as thedarker portion in the center. The lighter portion corresponds to plasmaregion 39.

FIG. 3 shows an isometric view of beam source 24 where certain watercooling piping is not shown. As described above, this water piping isuseful to make electrical connections to both electrodes. In theillustrated embodiment of FIG. 3, plasma 9 emanates outwardly fromnozzle 6 into the process chamber. As shown, plasma 9 forms a narrowuniform beam extending outwardly from nozzle 6.

As those skilled in the art will appreciate, beam source 24 may comprisemany shapes, sizes, scales, and may include a plurality of materials.For example, in one embodiment source 24 was constructed as follows:Magnets 1 and 2 were ceramic type measuring about 1″ wide×about 4″long×about 1″ thick. Magnets 20 and 21 were about 1″ wide×about 2″long×about 1″ thick. Block 12 was formed from brass. Top cover 5 andnozzle 6 were formed of copper. The opening in nozzle 6 was about 0.75″wide×about 0.75″ deep×about 3.5″ long. Shunt 10 and shunt 11 were formedof mild steel. Liner 16 was formed of copper sheet bent into an ovalshape, with the long internal diameter of that oval measuring about1.5″. As those skilled in the art will appreciate, many variations andmodifications can be made regarding the dimensions and materials ofsource 24 without departing from the scope of Applicant's invention.

Beam source 24, and the plasma 9 generated therewith, have many usefulproperties, including the following measured values using the sourcedescribed immediately above:

Plasma 9 is very dense, with ion densities exceeding 10¹² per cm³ whenusing a DC power supply output of 1 kW at 300 V. The ion saturationcurrent was measured at over 100 mA for the source dimensions given andthese power supply settings. The current probe surface was positioned 5cm beyond the end of nozzle 6 blocking plasma 9. Electron current withthe probe grounded is greater than 1 A.

Plasma 9 is uniform over the length of the source, minus end effects atthe turnarounds. This is important for applications where uniformity ofdeposition, treatment, or etching is required, as it is in mostapplications. Substrate widths of 3 meters or greater can be uniformlyprocessed. In operation, plasma 9 appears as one cm wide uniform beamextending outwardly from nozzle 6.

Plasma beam source (“PBS”) 24 is not a sputter source. Rather, source 24is useful for PECVD, plasma treatment, or etching processes. Althoughsputtering of the liner material does occur, only minimal amounts ofsputtered material exit nozzle 6 for several reasons. First, themagnetron plasma region 8 (FIG. 1) is located deep inside the source.Sputtered liner material redeposits on the liner, the shunts 10 and 11and/or on the cover 5 and nozzle 6. Because the sputtered materialreadily condenses upon contact with a surface, source 24 includes a‘torturous path’ for sputtered material to exit the source. Second, byfeeding process gas into the discharge chamber above magnetron plasma 8,the flow of supply gas to the plasma 8 is directed away from nozzle 6,creating directional momentum effects opposing condensate flow out ofnozzle 6.

A low sputter rate of the source is actually observed in operation. Forexample, when depositing a PECVD Silicon Oxide coating, after severalmicrons of coating were deposited, the resulting coating appearedoptically clear. This clear coating was produced using a copper liner16. As those skilled in the art will appreciate, sputtered copper in amixture of oxygen and argon gases comprises a black coating. No suchblack coating was observed forming a silicon oxide coating on asubstrate using source 24.

Pure reactive gas can be ‘burned’ in source 24. Prior art high densityplasma sources implement filaments, low work function materials, orfield effect devices, to generate electrons. These sources typicallyfeed an inert gas, such as argon, into the source. Use of a reactive gassuch as oxygen inside the source tends to greatly shorten electronsource lifetimes. To accomplish a reactive process, these sources feedoxygen into the plasma outside the source, reacting a portion of theoxygen with the argon plasma emanating from the source. While theefficiency of such prior art sources is low, those sources arenevertheless used today for many processes because no alternativeexists.

In marked contrast, however, Applicant's beam source 24 the productionof a high density, pure oxygen plasma. This has advantages to severalprocesses. In addition, the vacuum pumping requirements are also reducedbecause argon flow requirements are not a factor when using source 24.

Applicant's beam source 24 can be operated over a wide range of processpressures. As is typical for magnetron type sources, the PBS can readilyoperate at pressures in the 1-100 mTorr region. In addition to thispressure range, operation can be extended down to the 10⁻⁵ Torr rangeused in evaporation processes. Such pressures may be used because nozzle6 limits gas conductance out of the source. By feeding the process gas27 into discharge cavity 26, the pressure inside discharge cavity 26 canbe sustained in the mTorr region, while outside the source the processchamber may be maintained at a much lower pressure. Also, process gasflow requirements are minimized because discharge cavity 26 can bemaintained in the required mTorr region with less gas 27 flow due to theconductance limitation presented by the narrow nozzle 6 opening.

Plasma beam 9 extends outwardly for 100's of mm from nozzle 6 dependingupon the free mean path inside the process chamber. At 3 mTorr forinstance, the beam extends at least 300 mm outwardly from nozzle 6.Formation of such a plasma beam allows beam source 24 to excel at manyapplications. For instance, non-planar substrates can be uniformly PECVDcoated, treated, etc.

Substrate 23 can be electrically isolated from beam source 24. Becausethe substrate is not part of the electrical circuit, the substrate canremain floating or be separately biased by a different power supply. Incertain embodiments, beam source 24 comprises a standard magnetron powersupply using variety of frequencies, including. DC, or AC from 0-100 MHzfrequencies. Special high voltage power supplies or RF supplies do nothave to be used. The connection to chamber ground can also be made toeither side of the power supply. In FIGS. 1-3, box 3 and cover 5 areconnected to ground. This is convenient for safety considerations.

FIG. 4 shows beam source 24 in a PECVD coating application. A mixture ofargon and oxygen 41 are delivered to source port 4 via tube 40. Amonomer gas 43 is released outside the source. A polymeric coating isdeposited onto substrate 23 by polymerization of monomer gas activatedby the ionized gas in plasma 9. Because of the conductance limitation ofnozzle 6, and because of the high density and directionality of theplasma 9 exiting through nozzle 6, the monomer gas 43 does not entersource 24. This is actually observed when, after a coating run, thedischarge cavity 26 of beam source 24 is essentially free of PECVDcoating.

The substrate 23 can comprise a multitude of materials and shapes. Suchsubstrates include, for example and without limitation, flexible webs,flat glass, three-dimensional shapes, metals, silicon wafers, and thelike. Other physical and process configurations are possible using beamsource 24. For example, one or more monomer gases can be introduced intothe discharge cavity 26 without immediate buildup problems. In addition,certain monomer gases, such as hydrocarbons, can be fed into the sourcefor extended periods. Beam source 24 may also perform other plasmaprocesses such as plasma treatment, surface cleaning, or reactive ionetching.

FIG. 5 shows beam source 24 used to react evaporant 29 in an electronbeam evaporation web coating application. Drum 25 carries web 23 overthe deposition region. Crucible 27 contains evaporant material 28.Electron beam source 26 projects beam 31 into crucible 27. Plasma 9 isdirected into the evaporant cloud 29 to promote reaction with theionized gas of the plasma 9. Shield 30 limits the interaction of plasma9 with the electron beam 31.

Using prior art methods, complicated hollow cathode sources have beenused to accomplish evaporant reactance. Hollow cathodes are inherentlynon-uniform as the plasma outside of the hollow cathode is onlydiffusion limited. With Applicant's beam source 24, the magnetic fieldlines 19 contain the electrons, and by electrostatic forces, the ionsare likewise contained in plasma region 9. Also as described above, beamsource plasma 9 is uniform over the substrate width due to the closeddrift nature of the electron containment.

FIG. 6 depicts the beam source 24 applied to a planetary box coaterapplication. In this view the source 24 is shown along its length ratherthan from an end view. In the illustrated embodiment of FIG. 6, plasmabeam 9 appears as a sheet of plasma. Source 24 is positionedsufficiently remotely from the substrate supporting planetary, at thebottom of the box coater for example, to allow room for other depositionsources, such as electron beam, or thermal evaporation sources, forinstance. By combining the beam source 24 with other deposition sources,coatings can be densified by the action of plasma 9. In certainembodiments, pure argon is used to densify a metal coating. In otherembodiments, a reactive gas is added to the argon.

A major advantage of Applicant's source over the prior art is theability to directly consume reactive gases, such as oxygen, in thesource. Prior art sources, due to the need for filaments or otherelectron generation means sensitive to consumption by a reactive gas,required the use of an inert gas in the source. In these prior artsources, the reactive gas was fed into the process chamber external tothe source. The necessarily poor efficiency of ionizing the reactive gasin the chamber rather than in the source itself requires high sourcepowers and high argon flow rates. In contrast, using beam source 24 toproduce a pure reactive plasma, or a combination of inert and reactiveas required, process efficiency is increased and the overall pumpingspeed needed to maintain the process at the correct pressure is reduced.As those skilled in the art will appreciate, excess argon need not bepumped away.

FIG. 7 shows beam source 24 disposed above a substrate 23, such as asilicon wafer. In the illustrated embodiment of FIG. 7, the stage 51supporting the wafer 23 is translated, i.e. moved, in the X and/or Ydirections to uniformly treat wafer 23 with plasma 9. In FIG. 7illustrated the ability to separately bias substrate 23 and source 24.Bias supply 52, in this case an AC supply of sufficient frequency topass current through the wafer 23, is connected to stage 51. Beam sourcesupply 17 produces plasma 9. Without the bias supply 52, the insulatingsubstrate 23 would normally rise to the characteristic floating voltageof plasma 9, i.e. typically between about −10 to about −70 volts for thebeam source 24 depending upon process conditions. By turning on biassupply 52, the voltage drop across the plasma dark space between theplasma 9 and substrate 23 can be changed, positively or negatively, to alevel required for the process. Because the substrate 23 is not anelectrode in beam source 24, it can be separately biased.

FIG. 8 shows two beam sources, 24 a and 24 b, used to a generate a largearea uniform plasma 91 over a substrate. In the illustrated embodimentof FIG. 8, the substrate comprises flexible web 23 drawn over roll 64.The two beam sources 24 a and 24 b are identical, except magnets 60 and61 of source 24 a, and the end magnets (not shown) in source 24 a aredisposed such that the south pole has a facing relationship with plasma91, while source 24 b has magnet 62 and 63 north poles facing inwardly.This configuration creates a sharing of magnetic fields between thesources and produces the closed plasma region 91 as shown.

FIG. 9 shows a section view of source 90 configured for a spacepropulsion application. The basic components of the magnetron electronsource and cusp magnetic field are the same as in earlier figures. Insource 90, the magnetic cusp fields 18 and 19 are created by annularelectromagnets 70 and 71. The electron source magnetron plasma 8 iscreated with the liner tube 16. Liner 16 is electrically isolated frombox 3 by insulator plate 72 and from electromagnet 71 by insulator ring73. The propellant gas 27 is introduced into gas cavity 79 through port92. Gas 27 then flows into discharge cavity 26 via gap 78 between liner16 and opposed electrode 5.

Cover electrode 5 is electrically isolated from round box 3 by insulatorplate 76. Cover 5 has a nozzle portion 6 that fits down into the annularopening in electromagnet 70. Liner 16 and cover 5 are connected acrosspower supply 74. The illustrated embodiment of FIG. 11 includes a DCsupply with the cathode terminal connected to liner 16. In otherembodiments, an AC or RF power supply is used. Box 3 is connect toground. When power supply 74 is turned on, and gas 27 is flowing intodischarge cavity 26, electrons created by magnetron plasma 8 are trappedin mirror field region of magnetic field 18, and plasmas 9 and 39 arecreated. Thrust is generated as the plasma 9 is expelled through nozzle6. One component of the thrust is generated by the magnetic nozzleeffect. After passing through magnetic mirror 39, electrons thenexperience a decrease in magnetic field strength as they move outwardlyfrom nozzle 6. In response to this negative gradient field, electronmotion is converted from thermal spinning to kinetic motion along theaxis of the field lines.

The electrons in turn electrostatically pull ions into accelerating awayfrom the source. Another form of ion thrust is produced if the magneticfield in region 18 is increased to confine ions, i.e. to a magneticfield strength exceeding at least 1000 Gauss. Under this condition, ionsare magnetically confined and heated by the radial electric field asthey pass through nozzle 6. As those electrons exit the nozzle, they areaccelerated by both the electrostatic repulsion from anode 5 and by themagnetic nozzle effect.

The electron confinement achieved using Applicant's source includesphysically limiting two of the possible three axial magnetic fieldelectron escape paths by liner 16. The three axial magnetic fieldregions include: (i) cone shaped compressed region 18, (ii) cone-shapedcompressed region 19, and (iii) planar disk compressed region 170. Whenliner 16 is connected as the cathode of a DC circuit, or is on anegative AC cycle of an AC power supply, electrons are electrostaticallyreflected from the liner's surfaces. As electrons attempt to reach theanode electrode 5, they travel by collisional diffusion across fieldlines 19 and through mirror region 39 to exit the source through nozzle6 before returning to cover 5. While diffusing across magnetic fieldlines, the electrons also spiral along these field lines. By configuringthe source so magnetic field lines 170 pass through liner 16, electronsmoving along these field lines remain electrostatically contained. Iffield lines 170 were allowed to pass through an electrically floatingsurface or opposed electrode 5, some number of electrons would escapethrough the compressed mirror of field lines 170. Allowing only oneaxial magnetic field region 18 to be open to electron escape increasesthe efficient use of electrons in creating and sustaining plasma plume9.

FIG. 10 shows beam source 100. In various embodiments, source 100 iscircular, annular, or extended length wise. In the illustratedembodiment of FIG. 10, source 100 includes rare earth magnets 1 and 2,and two power supplies 83 and 84. Power supply 83 connects cathode liner16 to box 3. Insulator 81 separate box 3 electrically from cover 5.Power supply 84 connects anode cover 5 to box 3. Box three is grounded.

Using the illustrated configuration of FIG. 10, the plasma potential canbe adjusted relative to ground. This is useful when applying the plasma9 to a grounded substrate. By increasing the plasma potential, the ionenergy striking the substrate is increased. FIG. 10 further illustratesprocess gas manifolds 80 built into cover 5. Small distribution holes 85conduct the gas 27 uniformly along the length of source 100 intodischarge cavity 26. Facing the magnets 1 and 2 toward each other in acusp arrangement, creates a strong mirror compression ratio in mirrorregion 39. With rare earth magnets 1 and 2, the field strength at themirror apex can exceed 500 Gauss. As electrons pass through this mirrorregion 39, they experience this strong field and their Larmor gyroradius is correspondingly small. Under these conditions, when the plasmais viewed from the end as in this section view, the plasma 9 widthpassing through nozzle 6 is very narrow, on the order of 3 mm.

This is an advantage over vertically directed magnets of Window andSavvides, Helmer, and others. A vertical magnet orientation is shown inanother preferred embodiment in FIG. 11. With vertically orientedmagnets, while a null region 25 is created above the magnetron confinedregion. 8, the field strength is typically less than 100 Gauss and theelectron Larmor gyro radius is larger. In the illustrated embodiment ofFIG. 10, shunt 10 is fitted into aluminum body 12. Shunt 10 reduces thesputter rate of liner 16, and evens out liner 16 sputtering to make theliner 16 last longer. While helpful in this regard, shunt 10 is notnecessary to the fundamental source operation.

Body 12 is water cooled by extruded holes 82. Insulators 14 and 86support cathode body 12 in box 3 and electrically isolate the cathode,i.e. body 12 and liner 16, from box 3. Source 100 may be rectangularhaving an extended length. End magnets, used to make both magnetic fieldregions 8 and 9 closed paths, are not shown in FIG. 10.

FIG. 11 shows beam source 1100 having vertically oriented magnets. Thismagnet configuration is representative of a Type II unbalanced magnetronmagnetic field as taught by Window and Harding. A range of magnet 97shapes, and discharge cavity 26 shapes, can be implemented within thescope of Applicant's invention. In the illustrated embodiment of FIG.11, magnets 97 create two confinement regions: magnetron confinement 95at cathode 98 surface 105, and mirror/nozzle confinement 93 throughnozzle 104.

As in other embodiments of Applicant's source, a magnetron electrongeneration region 101 is contained in a discharge cavity 103. Thedischarge cavity contains a null magnetic field region 95. A aperture104 in cover plate 91 has a centerline coincident with the axis ofmirror field 93.

Planar liner 98 is water cooled via gun drilled hole 99 and is fittedinto shunt 96. Magnets 97 and angled shunts 109, along with shunt 96produce the unbalanced magnetic field depicted. Planar cathode 98 andmagnet components 96, 97 and 109 are suspended by electrical insulators(not shown) in electrically floating box 90. Electrically floating coverplate 91 is fastened to box 90. Cover plate 91 is water cooled via holes92. Piping to direct water to the cover plate 91 and cathode 98 is notshown. Gas 27 is piped into box 90 through threaded hole 100. Gas 27flows around magnet shunt 96 and into discharge cavity 103.

When power supply 108 is turned on, a magnetron plasma 102 lights andsupplies electrons to mirror confinement region 106. Electrons caught inmirror confinement region 106 collide with gas 27 also attempting toexit through the nozzle 104 opening, and dense plasma 94 is created. Theillustrated embodiment of FIG. 11 includes a separate anode 107. Cover91 is not connected as an electrode in the electrical circuit. Cover 91comprises a conductance limitation to the exiting gas 27, forcing thegas to exit through the mirror confinement region 106 in nozzle 104.Given the high mobility of electrons, positioning the return electrode107 external to the source produces little noticeable change in sourceperformance after the source lights. Because the anode 107 is moredistant from the cathode 98, a pressure spike may be needed in cavity103, depending upon the base pressure and the ignition voltage of thepower supply 108 used, to ignite the plasma 102.

Once a conductive plasma 102 has ignited, the anode electrode can belocated in any location within the process chamber. When the anodeelectrode is the nozzle 104, some ion acceleration benefits can beobtained as described earlier. In illustrated embodiment of FIG. 11, theliner material comprises aluminum. Aluminum is a good secondary electronemitter when oxygen gas 27 is used. Moreover, the reactive product,alumina, formed on the cathode surface 105 sputters very slowly. Theseare advantages to beam source operation because a high electron currentfor a given power is generated and the cathode material 98 is slow to besputtered away.

Other materials having these properties may also be used. For example,when an argon plasma 94 is desired, carbon is a good cathode material.While not an exceptional secondary electron emitter, carbon sputtersvery slowly in argon. Note that FIG. 11 is a section view. Source 1100can be round, or rectangular, and can be extended to lengths longer than1 meter. The present invention enables many applications and processes;Several have been mentioned above. More will be apparent to thoseskilled in the art While several embodiments have been presented, manyothers are possible within the scope of the present invention.

1. A plasma source, comprising: a discharge cavity having a first width,wherein said discharge cavity includes a top portion and a wall portion.a nozzle disposed on said top portion and extending outwardly therefrom,wherein said nozzle is formed to include an aperture extending throughsaid top portion and into said discharge cavity, wherein said aperturehas a second width, wherein said second width is less than said firstwidth; at least one cathode electrode connected to said first powersupply, wherein said cathode electrode is capable of supporting at leastone magnetron discharge region within said discharge cavity; a pluralityof magnets disposed adjacent said wall portion, where in said pluralityof magnets create a null magnetic field point within said dischargecavity; a conduit, other than said aperture, disposed in said dischargecavity for introducing an ionizable gas into said discharge cavity. 2.The plasma source of claim 1, wherein said ionizable gas is injectedbetween said cathode and said nozzle within said discharge cavity. 3.The plasma source of claim 1, wherein said plurality of magnetscomprises one or more electromagnets.
 4. The plasma source of claim 1,wherein two of the three axial magnetic field regions adjacent to saidnull point pass through said cathode surface, and wherein the thirdaxial magnetic field comprises the mirror confinement region emanatingthrough said nozzle.
 5. The plasma source of claim 1, wherein said nullmagnetic field point is located along the center-line of said aperture.6. The plasma source of claim 1 wherein said cathode material comprisesa secondary electron emission coefficient greater than about
 1. 7. Theplasma source of claim 1, wherein said nozzle is interconnected withsaid first power supply such that said nozzle comprises an anode.
 8. Theplasma source of claim 1, wherein said nozzle is electrically floating.9. The plasma source of claim 1, wherein said nozzle is electricallyconnected to ground.
 10. The plasma source of claim 1, furthercomprising a second power supply, wherein said second power supply isconnected to said nozzle such that said nozzle comprises an anode. 11.The plasma source of claim 7, wherein said second power supply isselected from the group consisting of a DC power supply, an AC powersupply, and RF power supply.
 12. A plasma processing apparatus,comprising: a beam plasma source comprising a discharge cavity having afirst width, wherein said discharge cavity includes a top portion and awall portion; a nozzle disposed on said top portion and extendingoutwardly therefrom, wherein said nozzle is formed to include anaperture extending through said top portion and into said dischargecavity, wherein said aperture has a second width, wherein said secondwidth is less than said first width; a power supply, wherein said wallportion is interconnected to said power supply and wherein said wallportion comprises a cathode; a plurality of magnets disposed adjacent toand external to said discharge cavity, wherein said plurality of magnetscreate a null magnetic field point within said discharge cavity; aconduit, other than said aperture, disposed in said discharge cavity forintroducing an ionizable gas into said discharge cavity; a processchamber, wherein said beam plasma source is disposed within said processchamber; a substrate disposed within said process chamber, wherein saidsubstrate is external to said beam plasma source.
 13. The plasmaprocessing apparatus of claim 12, further comprising an anode disposedwithin said process chamber, wherein said anode is not physicallyattached to said plasma beam source.
 14. The plasma processing apparatusof claim 12, wherein said beam plasma source further comprises a cuspmagnetic field producing at least one magnetron confinement one withinsaid cathode cavity.
 15. A plasma processing apparatus, comprising: anenclosure defining a cavity, wherein said enclosure is formed to includea nozzle; a power supply interconnected with said enclosure such thatsaid enclosure comprises a cathode electrode; a cusp magnetic fielddefining a null magnetic field point disposed within said cavity;wherein said cusp magnetic field comprises a first portion and a secondportion, wherein said first portion creates a closed drift electronmagnetron confinement region within said cathode cavity, and whereinsaid second portion produces a mirror confinement region passing throughsaid nozzle.
 16. A method to treat a substrate with a plasma beam,comprising the steps of: providing a beam plasma source comprising adischarge cavity having a first width, wherein said discharge cavityincludes a top portion and a wall portion; a nozzle disposed on said topportion and extending outwardly therefrom, wherein said nozzle is formedto include an aperture extending through said top portion and into saiddischarge cavity, wherein said aperture has a second width, wherein saidsecond width is less than said first width; a power supply, wherein saidwall portion is interconnected to said power supply and wherein saidwall portion comprises a cathode; a plurality of magnets disposedadjacent to and external to said discharge cavity; a conduit, other thansaid aperture, disposed in said discharge cavity for introducing anionizable gas into said discharge cavity; providing a process chamber;disposing said beam plasma source within said process chamber; providinga substrate; disposing said substrate within said process chamber,wherein said substrate is external to said beam plasma source; creatingnull magnetic field point within said discharge cavity; introducing anionizable gas into said discharge cavity via said conduit; igniting aplasma within said discharge cavity; projecting said plasma through saidnozzle; directing said plasma onto said substrate.
 17. The method ofclaim 16, further comprising the steps of: generating a plurality ofelectrons within said discharge cavity, wherein a portion of saidplurality of electrons passing through said null magnetic field pointpass out of said discharge cavity through said nozzle.
 18. The method ofclaim 17, further comprising the step of forming three mirror magneticfield electron confinement zones within said discharge cavity, whereineach of said three mirror magnetic field electron confinement zonesextend outwardly from said null magnetic field point.
 19. The method ofclaim 18, wherein one of said mirror magnetic field electron confinementzones extends through said aperture.